1. Field of the Invention
The invention relates to control of transmit power in a packet radio network.
2. Description of the Related Art
One of the consequences of bearer-less packet access in B3G cellular networks is that power control (PC) for user packet transmissions mainly relies on open-loop power control, including initial power setting and self-adjustment likely on a packet-by-packet basis.
In B3G cellular networks, however, strict power restriction of mobile terminals can be expected. The performance of an open-loop PC, also referred to as PC accuracy, depends on the dynamic range of fading channel conditions and capabilities and the performance of link adaptation schemes.
A need will arise for a fade-margin setting in an open-loop PC operation in order to assure a reliable and robust radio performance over fading channels. The fade margin can be defined as a margin between a specified target signal level and a local root-mean-square amplitude of the fading envelope. The smaller the fade margin is, the lower the additional transmit power is needed to combat the impact of fading. The fade margin is usually set by the network to be equal for all mobile terminals.
Currently, the network estimates a proper value for the fade margin based on the amount of traffic and measurement results regarding transmitted data packets. This kind of estimation does not provide an adequately precise basis for determining a fade margin parameter, which thereby results in non-optimal usage of the network.